[sdiy] S&H

[Scott Bernardi]

Why not use a MOSFET input opamp? Like the CA3140?

Roman wrote:

> Drop caused by SH cap is nothing to worry about in comparison with
> buffer opamp leakage. I'm trying now to make S&H and I must say I
> dropped the idea of using opamp as a buffer long time ago. MOSFET can
> be about 10 times better than low bias opamp. Some of them have gate
> current below 1pA, best I tested - about 1/4pA. It was BSS138 if I
> remember right.
>
> Roman
>
> Tim Ressel <madhun2001 at yahoo.com>:
>
> >John,
> >
> >Um, I'm not sure. I ain't no S&H expert, I just play
> >one on TV. That's why I sed to check out datasheets
> >and app notes. I know that there is a way to include
> >the SH cap in the feedback path of the opamp to
> >prevent droop.
> >
> >--tr
> >
> >--- John L Marshall <john.l.marshall at gte.net> wrote:
> >> Tim,
> >>
> >> Can't the droop be compensated for by a second
> >> capacitor in the feedback
> >> path of the buffer opamp?
> >>
> >>
> >> Take care,
> >> John
> >>
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